High speed token ring networks are often used to interconnect high performance computers and peripheral equipment. Such rings can also be used as a backbone transmission facility to interconnect local area networks (LANs). A token ring is a closed ring configuration in which a special frame, called the "token," is circulated and used to control access of multiple stations on the ring to the ring transmission facility. The protocol allows a newly active station to seize the transmission facility when the token is received at that station. The active station then transmits the data originated at that station and intended for another station on the ring. In order to provide fair access to the transmission facility, no station is allowed to hold the token longer than a specific amount of time, called the token holding time (THT). When the token holding time expires, the transmitting station must relinquish the token to allow other stations to seize the token and transmit their own data.
If there is only one active station on a token ring, the requirement to relinquish the token results in an idle period while the token circulates around the ring looking for another newly active station when no such newly active station exists. This idle period, equal to the latency time of the ring, limits the overall throughput of the the ring network and thus reduces the efficiency of the network. Moreover, the shorter the token holding time (in order to support larger numbers of users, support real-time applications, or merely to provide better sharing of the transmission facility), the larger the inefficiency.